It is now technically possible to examine malignant and non- malignant prostatic tissue both directly and after tissue culture for (a) morphologic differences and (b) viral particle presence. It is similarly possible to examine prostatic fluid and semen and tissue culture fluid for the physical presence of viral particles. We propose to obtain malignant and non-malignant prostatic tissue at surgery. This tissue will be prepared for light and electron microscopy. Other portions will be established in tissue culture. Prostatic secretions and semen will be obtained from patients with biopsy-proven carcinoma of the prostate and from normal controls. Culture fluid will be obtained from tissue cultures of malignant and non-malignant prostatic cells. Efforts will be directed toward identifying virus particles in these tissues and fluids. Particulate material from culture fluids, from prostatic secretions and from semen will be studied by quantitative particle enumeration, by negative staining and in thin sections of centrifugal pellets for evidence of virus. Cultures treated with agents as iododeoxyuridine or radiation (to promote virus elaboration by cells carrying an unexpressed virus genome) and non-malignant prostatic tissue after exposure to known oncogenic viruses will be similarly examined.